Fix IP checksum offload metadata setup

Change-Id: Idf4f8b02337551670d6b7ce1a03799de9c53d19a
Signed-off-by: Dave Barach <dave@barachs.net>
diff --git a/src/vnet/ip/ip4.h b/src/vnet/ip/ip4.h
index 19198bc..872b516 100644
--- a/src/vnet/ip/ip4.h
+++ b/src/vnet/ip/ip4.h
@@ -347,8 +347,18 @@
   ih->src_address.as_u32 = src->as_u32;
   ih->dst_address.as_u32 = dst->as_u32;
 
-  ih->checksum = 0;
-  b->flags |= VNET_BUFFER_F_OFFLOAD_IP_CKSUM | VNET_BUFFER_F_IS_IP4;
+  /* Offload ip4 header checksum generation */
+  if (1)
+    {
+      ih->checksum = 0;
+      b->flags |= VNET_BUFFER_F_OFFLOAD_IP_CKSUM | VNET_BUFFER_F_IS_IP4;
+      vnet_buffer (b)->l3_hdr_offset = (u8 *) ih - b->data;
+      vnet_buffer (b)->l4_hdr_offset = vnet_buffer (b)->l3_hdr_offset +
+	sizeof (*ih);
+    }
+  else
+    ih->checksum = ip4_header_checksum (ih);
+
   return ih;
 }
 #endif /* included_ip_ip4_h */